Optical head, and optical recording and reproducing apparatus

ABSTRACT

An optical head has a near-field light generating element generating near-field light; and a beam shaper which shapes an incident beam into a substantially coroidal beam and directs the shaped beam to said near-field light generating element. According to the optical head having the above-described structure, the incident light is shaped into a substantially toroidal beam without being intercepted, incident on the zonal part of the near-field light generating element, and condensed to a minute spot. That is, only the light of the high numerical aperture part is used with efficiency, and the light can be condensed to a minute spot.

RELATED APPLICATION

[0001] This application is based on application No. 2000-39522 filed inJapan, the content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an optical head, particularly,an optical head for performing recording, reproduction and erasure byuse of near-field light, and an optical recording and reproducingapparatus having the optical head.

DESCRIPTION OF THE PRIOR ART

[0003] In recent years, to realize high density recording by usinglight, a solid immersion technology has been proposed. This technologyis to form a minute light spot of not more than 100 nm by reducing thewavelength of light by disposing a high refractive index materialbetween an objective lens and a record medium. As the high refractiveindex material, although liquid (oil or water) is frequently used in thefield of high resolution microscopes, in the field of optical recording,a solid immersion lens or a solid immersion mirror is used to form anoptical head.

[0004] In such an optical head, a solid immersion lens or a solidimmersion mirror is disposed at a distance shorter than the wavelengthof light from the surface of the record medium so that the numericalaperture (NA) of light condensation is large, that is, the spot of lightcondensation is small, thereby realizing high density recording.

[0005] In this type of optical head, when some configurations of solidimmersion mirrors are used, it is desirable to use only the zonal partof the incident beam without using the central part thereof. Moreover,there are cases where it is desirable to use only light of the highnumerical aperture part in order that the spot of light condensation issmall on the solid immersion lens or the solid immersion mirror. Toobtain such incident light, it is considered to intercept the centralpart of the beam. However, this reduces the efficiency of use of light,which leads to reduction in the efficiency of recording and the like andreduction in speed.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide an improvedoptical head and optical recording and reproducing apparatus.

[0007] Another object of the present invention is to provide an opticalhead and an optical recording and reproducing apparatus in which theefficiency of use of light is increased to solve the problems ofreduction in the efficiency of recording and the like and reduction inspeed.

[0008] The above-mentioned objects are achieved by an optical headcomprises a near-field light generating element which generatesnear-field light; and a beam splitter which splits an incident lightinto a plurality of beams and directs the split beams to said near-fieldlight generating element.

[0009] According to the optical head having the above-describedstructure, the light emitted from the light source portion is split intoa plurality of beams, incident on the zonal part of the near-field lightgenerating element, and condensed inside the element. Consequently, thelight emitted from the light source portion is effectively used withoutbeing intercepted, and the light can be condensed to a minute spot, thatis, the numerical aperture can be increased.

[0010] Moreover, an optical head of another structure comprises anear-field light generating element which generates near-field light;and a beam shaper which shapes an incident beam into a substantiallytoroidal beam and directs the shaped beam to said near-field lightgenerating element.

[0011] According to the optical head having the above-describedstructure, the light emitted from the light source portion is shapedinto a substantiallytoroidal beam without being intercepted, incident onthe zonal part of the near-field light generating element, and condensedto a minute spot. That is, only the light of the high numerical aperturepart is used with efficiency, and the light can be condensed to a minutespot.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] This and other objects and features of this invention will becomeclear from the following description, taken in conjunction with thepreferred embodiments with reference to the accompanied drawings inwhich:

[0013]FIG. 1 schematically shows the structure of an optical recordingand reproducing apparatus according to an embodiment of the presentinvention;

[0014]FIG. 2 is an explanatory view showing operation of a solidimmersion mirror;

[0015]FIG. 3 is an explanatory view showing operation of a solidimmersion lens;

[0016]FIG. 4 is an explanatory view showing a first example of beamshaper;

[0017]FIG. 5 is an explanatory view showing a second example of the beamshaper;

[0018]FIG. 6 is an explanatory view showing a third example of the beamshaper;

[0019]FIG. 7 is an explanatory view showing a fourth example of the beamshaper;

[0020]FIG. 8 is an explanatory view showing a fifth example of the beamshaper;

[0021]FIG. 9 is an explanatory view showing a sixth example of the beamshaper;

[0022]FIG. 10 is an explanatory view showing a seventh example of thebeam shaper;

[0023]FIG. 11 is an explanatory view showing an eighth example of thebeam shaped;

[0024]FIG. 12 is an explanatory view showing an example of beamsplitter; and

[0025]FIG. 13 is an explanatory view showing the condition of lightapplication to the solid immersion mirror by the beam splitter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Hereinafter, an embodiment of the optical head and the opticalrecording and reproducing apparatus according to the present inventionwill be described with reference to the attached drawings.

[0027] Optical Recording and Reproducing Apparatus, Referring FIG. 1

[0028]FIG. 1 shows an optical recording and reproducing apparatus 1according to an embodiment of the present invention. The apparatus 1mainly includes a light source portion 2, a plane mirror 5 and anoptical head 10. The light source portion 2 is a known one comprising alaser diode 3 as a light source and a collimator lens 4. The opticalhead 10 comprises a beam shaper 11 and a solid immersion mirror 12.

[0029] The laser beam L emitted from the laser diode 3 is collimated bythe collimator lens 4 and reflected at the mirror 5 to be directed tothe optical head 10. Then, the laser beam L is shaped into a toroidalbeam L1 by the beam shaper 11, incident on the solid immersion mirror12, condensed on the bottom surface of the mirror 12 and oozes out asnear-field light. The near-field light is applied to an optical recordmedium 18.

[0030] The optical record medium 18 is a known one having a recordinglayer and a protective layer formed on the surface thereof. The opticalrecord medium 18 is clamped to the rotation shaft of a spindle motor 19and rotated about a shaft center C at a predetermined speed. The opticalhead 10 moves along the radius of the optical record medium 18 at aconstant speed to perform recording, reproduction or erasure on theentire surface of the recording layer.

[0031] The structure and operation of the beam shaper 11 and the solidimmersion mirror 12 will be described below. The beam shaper 11 and thesolid immersion mirror 12 may be replaced by beam splitter 13 and asolid immersion lens 14 described below.

[0032] Solid Immersion Mirror, Referring to FIG. 2

[0033]FIG. 2 shows the solid immersion mirror 12 for generatingnear-field light. The solid immersion mirror 12 is made of a highrefractive index material, and comprises a first surface (top surface)being plane and a second surface (bottom surface) being spherical oraspherical. A reflecting film 12 a is formed in the center of theincident surface, and a reflecting film 12 b is formed in the peripheralzonal part of the bottom surface.

[0034] On the top surface of the solid immersion mirror 12, the toroidalbeam L1 shaped by the beam shaper 11 is incident. The beam L1 isreflected at the reflecting film 12 b to be converged, further reflectedat the reflecting film 12 a to be condensed to a minute spot at thecenter of the bottom surface, and oozes out as near-field light.

[0035] Solid Immersion Lens, Referring to FIG. 3

[0036]FIG. 3 shows the solid immersion lens 14 for generating near-fieldlight like the solid immersion mirror 12. The solid immersion lens 14 isalso made of a high refractive index material, and comprises a firstsurface (incident surface) being hemispherical (the first surface maybehyperhemispherical) and a second surface (bottom surface, exitsurface) being plane. Immediately above the solid immersion lens 14, acondenser lens 15 is disposed.

[0037] Various modes are present in which a laser beam is made incidenton such a solid immersion lens 14. In this example, when thetoroidalbeam L1 shaped by the beam shaper 11 is made incident through thecondenser lens 15, the beam L1 is refracted to be converged, condensedto a minute spot at the center of the bottom surface, and oozes out asnear-field light. The reason why the beam L1 beingtoroidal is madeincident is thata minute light condensation spot can be formed by usinglight of the high numerical aperture part.

[0038] First Example of Beam Shaper, Referring to FIG. 4

[0039] This beam shaper 11 comprises a firstaxicon lens 21 and a secondaxicon lens 22 coaxially disposed sothat convex conical surfaces 21 aand 22 a thereof are opposed to each other. The parallel laser beam Lbeing incident on the firstaxicon lens 21 so that the axis thereofcoincides with the optical axis of the lens 21 is refracted at theconical surface 21 a, intersects at the axis center and is then shapedinto a radially spreading beam being toroidal in cross section. Then,the beam L is incident on the secondaxicon lens 22 to be refracted atthe conical surface 22 a, shaped into the parallel tubular beam L1 beingtoroidal in cross section, and incident on the zonal part of the topsurface of the solid immersion mirror 12.

[0040] Second Example of Beam Shaper, Referring to FIG. 5

[0041] This beam shaper 11 comprises a firstaxicon lens 23 and a secondaxicon lens 22 coaxially disposed so that concave and convex conicalsurfaces 23 a and 22 a thereof are opposed to each other. The parallellaser beam L being incident on the firstaxicon lens 23 so that the axisthereof coincides with the optical axis of the lens 23 is refracted atthe conical surface 23 a, and shaped into a radially spreading beambeingtoroidal in cross section. Then, the beam L is incident on thesecondaxicon lens 22 to be refracted at the conical surface 22 a, shapedinto the parallel tubular beam L1 beingtoroidal in cross section, andincident on the zonal part of the top surface of the solid immersionmirror 12.

[0042] Third Example of Beam Shaper, Referring to FIG. 6

[0043] This beam shaper 11 uses a single lens 25 to shape the laser beamL into the toroidal beam L1. The lens 25 is formed as a double coneprism having convex conical surfaces 25 a and 25 b at the top andbottom. The parallel laser beam L is refracted at each of the conicalsurfaces 25 a and 25 b, shaped into the parallel tubular beam L1 beingtoroidal in cross section, and incident on the zonal part of the topsurface of the solid immersion mirror 12.

[0044] Fourth Example of Beam Shaper, Referring to FIG. 7

[0045] This beam shaper 11 uses a single lens 26 to shape the laser beamL into the toroidal beam L1 like the third example. The lens 26 isformed as a double cone prism having a concave conical surface 26 a atthe top and a convex conical surface 26 b at the bottom. The parallellaser beam L is refracted at each of the conical surfaces 26 a and 26 b,shaped into the parallel tubular beam L1 beingtoroidal in cross section,and incident on the zonal part of the top surface of the solid immersionmirror 12.

[0046] Fifth Example of Beam Shaper, Referring to FIG. 8

[0047] This beam shapre 11 comprises two Fresnel lenses 31 and 32combined in parallel with the lens surfaces thereof opposed to eachother. The Fresnel lenses 31 and 32 act similarly to the axicon lenses21 and 22. The parallel laser beam L is refracted at each of the Fresnellenses 31 and 32, shaped into the parallel tubular beam L1 beingtoroidal in cross section, and incident on the zonal part of the topsurface of the solid immersion mirror 12.

[0048] In the fifth example, instead of theFresnel lenses 31 and 32,transmission-type diffraction optical elements using a hologram or thelike and having similar functions to the Fresnel lenses 31 and 32 may beused. In the beam shaper 11 of the first to the fourth examples, theaxicon lenses may be replaced by diffraction optical elements such asFresnel lenses.

[0049] Sixth Example of Beam Shaper, Referring to FIG. 9

[0050] This beam shaper 11 uses reflection, and comprises a mirror 41having a conical reflecting surface 41 a and a ring-shaped mirror 42having a conical reflecting surface 42 a on the inner surface thereof.The parallel laser beam L being incident on the mirror 41 through thecentral opening of the ring-shaped mirror 42 is reflected at thereflecting surfaces 41 a and 42 a, shaped into the parallel tubular beamL1 beingtoroidal in cross section, and incident on the zonal part of thetop surface of the solid immersion mirror 12.

[0051] By forming the beam shaper 11 by use of reflection-type elementsas described above, generation of chromatic aberration can be prevented.

[0052] Seventh Example of Beam Shaper, Referring to FIG. 10

[0053] This beam shaper 11 also uses reflection, and comprises a singlemirror 43 having conical reflecting surfaces 43 a and 43 b. The parallellaser beam L being incident on the central part of the mirror 43 isreflected at the reflecting surfaces 43 a and 43 b, shaped into theparallel tubular beam L1 beingtoroidal in cross section, and incident onthe zonal part of the top surface of the solid immersion mirror 12.

[0054] In the sixth and the seventh examples of the beam shaper 11, thereflecting surfaces of the mirrors 41, 42 and 43 do not necessarily havethe illustrated configurations but may be, for example, reflectingsurfaces having a configuration of an aggregation of concentric coneslike Fresnel lenses. Further, reflection-type diffraction opticalelements using a hologram may be used.

[0055] Eighth Example of Beam Shaper, Referring to FIG. 11

[0056] This beam shaper 11 is formed integrally with the solid immersionmirror generating near-field light. Specifically, the mirror 43 shown inthe seventh example and the solid immersion mirror 12 are cementedtogether. The conical space formed in the center is left hollow orfilled with a different medium. The beam shaper 11 and the solidimmersion lens may be integrated to form an optical head.

[0057] Beam Splitter, Referring to FIGS. 12 and 13

[0058] Next, an example of the beam splitter 13 used instead of the beamshaper 11 will be described. The beam splitter 13 comprises, as shown inFIG. 12, oneplaneparallel mirror 51 having a partially reflectingsurface 51 a and a totally reflecting surface 51 b.

[0059] Part of the parallel laser beam L emitted from the light sourceportion 2 is reflected at the partially reflecting surface 51 a to beincident in a spot shape on a zonal part 12 c of the solid immersionmirror 12 as a beam L2. Part of the laser beam L transmitted by thepartially reflecting surface 51 a is reflected at the totally reflectingsurface 51 b to be incident in a spot shape on the zonal part 12 c ofthe solid immersion mirror 12 as a beam L3.

[0060] By using one planeparallel mirror 51 as described above, thelaser beam L can be split into the two beams L2 and L3 so as to beincident on the zonal part 12 c of the solid immersion mirror 12.Further, by adding anotherplaneparallel mirror, as shown in FIG. 13,beams L4 and L5 can be made incident on the zonal part 12 c. The numberof combinations of planeparallel mirrors may be three or more.

[0061] As the beam splitter 13, various splitter may be used as well asaplaneparallel mirror. Moreover, the beam splitter 13 and the solidimmersion lens 14 may be combined to form an optical head.

[0062] Other Embodiments

[0063] The optical head and the optical recording and reproducingapparatus according to the present invention are not limited to theabove-described embodiment, but various changes and modifications may bemade without departing from the spirit and scope of the invention.

[0064] While the beam shaper is combined with a solid immersion mirrorin the first to the eighth examples of the beam shaper, it may becombined with a solid immersion lens. Moreover, the optical recordingand reproducing apparatus may be used as a master plate exposingapparatus manufacturing master plates of optical record media.

[0065] Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodification depart from the scope of the present invention, they shouldbe construed as being included therein.

What is claimed is:
 1. An optical head comprising: a near-field lightgenerating element generating near-field light; and a beam shaper whichshapes an incident beam into a substantiallycoroidal beam and directsthe shaped beam to said near-field light generating element.
 2. Anoptical head as claimed in claim 1 , wherein the near-field lightgenerating element is a solid immersion lens element.
 3. An optical headas claimed in claim 1 , wherein the near-field light generating elementis a solid immersion mirror element.
 4. An optical head as claimed inclaim 1 , wherein the beam shaper has a first axicon lens and asecondaxicon lens coaxially disposed so that convex conical surfaces andthereof are opposed to each other.
 5. An optical head as claimed inclaim 1 , wherein the beam shaper has a first axicon lens and asecondaxicon lens coaxially disposed so that concave and convex conicalsurfaces and thereof are opposed to each other.
 4. An optical head asclaimed in claim 1 , wherein the beam shapers a single lens elementformed as a double cone prism having convex conical surfaces and at thetop and bottom.
 5. An optical head as claimed in claim 1 , wherein thebeam shaper is a single lens element formed as a double cone prismhaving a concave conical surface at the top and a convex conical surfaceat the bottom.
 6. An optical head as claimed in claim 1 , wherein thebeam shaper is two Fresnel lenses and combined in parallel with the lenssurfaces thereof opposed to each other.
 7. An optical head as claimed inclaim 1 , wherein the beam shaper is a transmission-type diffractionoptical element.
 8. An optical head as claimed in claim 1 , wherein thebeam shaper has a mirror having a conical reflecting surface and aring-shaped mirror having a conical reflecting surface on the innersurface thereof.
 9. An optical head as claimed in claim 1 , wherein thebeam shaper is a single mirror elements having conical reflectingsurfaces.
 10. An optical head as claimed in claim 1 , wherein the beamshaper formed integrally with the solid immersion mirror generatingnear-field light.
 11. An optical head as claimed in claim 1 , whereinthe beam shaper has one planeparallel mirror having a partiallyreflecting surface 51 a and a totally reflecting surface.
 12. An opticalhead comprising: a near-field light generating element which generatesnear-field light; and a beam splitter which splits an incident lightinto a plurality of beams and directs the split beams to said near-fieldlight generating element.
 13. An optical head as claimed in claim 12 ,wherein the near-field light generating element is a solid immersionlens element.
 14. An optical head as claimed in claim 12 , wherein thenear-field light generating element is a solid immersion mirror element.15. An optical apparatus comprising: a light source which emits a beam;and an optical head, having a near-field generating element generatingnear-field light emitted from the light source; and a beam shaper whichshapes an incident beam into a substantially toroidal beam and directsthe shaped beam to said near-field light generating element.
 16. Anoptical apparatus as claimed in claim 15 , wherein the near-field lightgenerating element is a solid immersion lens element.
 17. An opticalapparatus as claimed in claim 15 , wherein the near-field lightgenerating element is a solid immersion mirror element.
 18. An opticalapparatus comprising: a light source which emits a beam; and an opticalhead, having a near-field generating element generating near-field lightemitted from the light source; and a beam splitter which splits anincident light into a plurality of beams and directs the split beams tosaid near-field light generating element.
 19. An optical apparatus asclaimed in claim 18 , wherein the near-field light generating element isa solid immersion lens element.
 20. An optical apparatus as claimed inclaim 18 , wherein the near-field light generating element is a solidimmersion mirror element.